When I use BIAB I get different grain absorption rates with different grain bills. For instance wheat doesn't absorb much at all. In order to try and have consistency with my process, I decided to not guess my absorption rate and just stick with 4.5 gallons pre mash every time.

I told this to my LHBS (great guy) and he said instead I should try to focus on getting the same amount volume of pre boil and post boil liquid. He says this would be a better thing to tighten up my process. But seeing as I am having a hard time doing that, I don't know what I should do.

Can I get some thoughts and advice on this? By the way I usually get around 80% efficiency.

I'm on the low end of procedures that call for permission. However I'm getting much better over time at close to equal runnings and pre and post boil volumes. I have a big ss stir spoon that is marked at six gallons and seven gallons. Harder to explain than it is to do, but basically I ballpark my absorption at a gallon per ten pounds. I add that extra absorption water to my mash then brew away. I start one hour boils with six gallons and adjust from there for more boil time or more than normal hops. My IPA starts with seven gallons. I usually hit 5 gallons at the end, or pretty close.

Do you squeeze your bag? That should help even out the differences between different grain bills. I honestly don't factor in a difference in absorption at all regardless of my grain bill. I probably get a bigger variation in my boiloff rate than my absorption. But I'm pretty laid back about the my brews. If I miss my OG by 2-3 points it's no big deal.

Thanks for the replies guys. Yes I do squeeze the bag. And my efficiency is mash not brew house. I have measured my grain absorption to be 0.07 gallons/lb of grain, however sometimes its .10 and sometimes its .03 (with the wheat).

I guess if i dont have as much grain absorption I can add water to my preboil so i can focus on keeping the volumes of pre/post boil the same, but will that mess with my OG anyways lol?